一道难死人的小学奥数题
来源:学生作业帮 编辑:神马作文网作业帮 分类:数学作业 时间:2024/11/17 12:14:13
一道难死人的小学奥数题
1/3+1/(3+6)+1/(3+6+9)+1/(3+6+9+12)+…+1/(3+6+9+12+…99)
1/3+1/(3+6)+1/(3+6+9)+1/(3+6+9+12)+…+1/(3+6+9+12+…99)
1/3+1/(3+6)+1/(3+6+9)+...+1/(3+6+9+...+99)
=1/3+1/[3*(1+2)]+1/[3*(1+2+3)]+...+1/[3*(1+2+3+...+33)]
=2/3*[1/(1*2)+1/(2*3)+1/(3*4)+...+1/(33*34)]
=2/3*[1-1/2+1/2-1/3+1/3-1/4+...+1/33-1/34]
=2/3*[1-1/34]
=11/17
=1/3+1/[3*(1+2)]+1/[3*(1+2+3)]+...+1/[3*(1+2+3+...+33)]
=2/3*[1/(1*2)+1/(2*3)+1/(3*4)+...+1/(33*34)]
=2/3*[1-1/2+1/2-1/3+1/3-1/4+...+1/33-1/34]
=2/3*[1-1/34]
=11/17